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Abstract

Exercise interventions in those with an implantable cardioverter defibrillator (ICD) have not been extensively studied. Health care providers are often reluctant to prescribe exercise for this group because:

they are unsure how to define and monitor safe exercise parameters, and

there is a belief that exercise will provoke ventricular arrhythmias and ICD shocks. Patients are often afraid to exercise because of the concern for receiving an ICD shock.

The purpose of this paper is to outline a method for safely prescribing exercise in patients who have an ICD using parameters derived from the cardiopulmonary exercise test (CPET).

Methods. A RCT of aerobic exercise vs. usual care for persons with an ICD was used. Each person completed 2 CPETs to determine maximal oxygen consumption (VO2 max) at baseline and 8 weeks later. Individualized exercise prescriptions were based on the baseline CPET using the Karvonen formula for heart rate reserve (HRR): Target Heart Rate (THR)=[(HRMax−HRRest) × Intensity + HRRest]. To achieve an aerobic training effect, exercise was prescribed at 60% of HRR for 2 weeks, 70% of HRR for 2 weeks, and 80% of HRR for the last 4 weeks. An individually programmed Polar Heart Rate Watch (RS400) with the specific THR was exchanged every 2 weeks. Heart rate is sampled every 15 seconds during exercise sessions and is saved in the Polar Watch. Exercise sessions are downloaded and % time above, within, and below the THR are derived.

Results. 151 CPET’s were performed with 72 persons, with an average age of 57.3±11.9 years old, 90% Caucasian, 81% male, and mean EF%= 40.7±15.6 and mean Charlson score=1.4±12. All participants were taking beta blocker medication during the study. There are no ICD shocks, hospitalizations, HF exacerbations, MIs, deaths, ER visits, cardiac arrests or new or unstable angina associated with either the CPET protocol or with performance of exercise. One episode each of non-sustained VF or VT was noted in the recovery period after the CPET. THR was achieved 67% of the time.

Conclusions. A safe CPET can be performed and aerobic exercise safely prescribed and monitored in persons with ICDs. The Karvonen formula for HRR is somewhat aggressive and not achieveable for everyone who is taking beta blocker medication.